Developing device for electrophotography

ABSTRACT

A magnetic brush developing device provided with hard brush directly formed on the magnet surface and soft brush formed on the hard brush. The brush is so shaped that the hard brush does not scrub the image forming surface and the soft brush will develop the image.

United States Patent [1 1' Katayama et al.

[451 May 13, 1975 DEVELOPING DEVICE FOR ELECTROPHOTOGRAPHY Inventors: Hajime Katayama, Kawasaki; Toru Takahashi, Tokyo, both of Japan Canon Kabushiki Kaisha, Tokyo, Japan Filed: Mar. 12, 1973 Appl. No.: 340,299

Related US. Application Data Continuation of Ser. No. 276,312, July 31, 1972, abandoned, which is a continuation of Ser. No. 16,288, March 4, 1970, abandoned.

Assignee:

US. Cl. 118/637; 355/3 DD Field of Search 118/637; 117/175;

References Cited UNITED STATES PATENTS Keller et a1. 1 18/637 3,152,924 10/1964 Wanielista et a1. 118/637 3,233,586 2/1966 Cranskens et al. 118/637 3,233,587 2/1966 Morton 118/637 3,387,586 6/1968 Shelffo et a1.. 117/17.5 X 3,455,276 7/1969 Anderson 118/6'37 3,552,355 1/1971 Flint 118/637 X FOREIGN PATENTS OR APPLICATIONS 17,228 8/1965 Japan 118/637 Primary Examiner-Morris Kaplan Attorney, Agent, or FirmFitzpatrick, Cella, Harper & Scinto [57] ABSTRACT A magnetic brush developing device provided with hard brush directly formed on the magnet surface and soft brush formed on the hard brush. The brush is so shaped that the hard brush does not scrub the image forming surface and the soft brush will develop the image.

4 Claims, 4 Drawing Figures PATENIED 1m 1 3197s SHEH 10F 2 FIG.I

FIG. 2

PATENIED HAY I 3 I975 SHEET 20$ 2 FIG. 4

DEVELOPING DEVICE FOR ELECTROPHOTOGRAPHY This is a continuation of application Ser. No. 276,312, filed July 31, 1972, which in turn was a continuation of application Ser. No. 16,288, filed Mar 4, l970, each application now abandoned.

BACKGROUND OF THE INVENTION:

The present invention relates generally to a developing device for electrophotography and more particularly to a developing device of the type in which an electrostatic latent image formed upon a photosensitive member by an electrophotographic copying machine is developed by use of a magnetic brush.

The methods for developing an electrostatic latent image formed upon a photosensitive member such as sensitized plate or copy paper in an electrophotographic copying machine are classified generally into two methods, one being a dry type developing method and the other, a wet type developing method. In the dry developing method, the electrostatic latentimage formed. upon the photosensitive member may be developed by applying the toner upon the photosensitive member. The applied toner is attracted by the electrostatic charge-of the latent image and the resultant toner image may be transferred to the surface of a suitable recording member, such as paper, by heating or adding the vapor of a solvent so as to fix the toner and adhere it to the paper or the like. Alternatively, the toner image developed upon the photosensitive member may be fixed thereto. A wide variety of dry developing methods, such as the toner spraying method, the cascade method, magnetic brush method, the powder cloud method and so on have been proposed and used.

Of these methods, the present invention contemplates an improvement of the magnetic brush developing method.

In the conventional magnetic brush developing process, the image developing surface of the photosensitive member is directly scrubbed by brush formed directly upon a magnet or hard brush, but there is a serious problem that when the image is developed by the hard brush, the toner image is scrubbed off the photosensitive member, so that the toner image is distorted or deformed. In the conventional magnetic brush developing device, having only one magnetic roller, it is very difficult to distribute the toner on the magnetic brush so as to uniformly adhere the toner to the brush and to uniformly impart the charge to the toner. Therefore, the potential of the charge imparted to the toner is low so that the developed image has a low tone and fogging occurs in the white parts of the image. Furthermore, the poles arranged around the outer peripheral surface of the magnetic roller are generally spaced apart from each other by'a relatively considerable distance, so that magnetic brushes are formed in spaced apart relation with each other, thereby causing devel oping marks.

SUMMARY OF THE INVENTION In view of the above, the primary object of the present invention is to provide an improved magnetic brush image forming surface of the photosensitive member, thereby preventing the scrubbing of the toner image formed thereupon by the hard brush.

A further object of the present invention is to provide an improved magnetic brush developing device in which a soft brush is formed upon a hard brush which is directly formed upon the surfaces of magnets so as to develop an image by this soft brush.

A still further object of the present-invention is to provide an improved magnetic brush developing device in which a soft brush can be fonned in a more positive and concrete manner upon a hard brush which is formed directly upon the surfaces of the magnets. An another object of the present invention is to provide an improved magnetic brush developing device in which a plurality of magnetic brushes are formed in parallel with each other so that the hard and soft brushes may scrub each other.

The object of the present invention is to improve the quality of the images developed. To improve the image quality by increasing the resolution power and eliminating fogging, the intimate contact between the image forming surface of the photosensitive member and the magnetic brush must be ensured. To this-end, in the developing device in accordance with the present invention the magnetic brush consists of hard and soft brushes and the thickness and the strength of the magnetic brush are so determined that the optimum contact of the brush with the image forming surface may be attained with a force which does not scrub off the toner image once formed upon the image forming surface of the photosensitive member. In order to facilitate the mixing of the toner into and the scrubbing of the toner. with the magnet brush, a plurality of magnet brushes are disposed in parallel with each other so that the adjac'en'tbrushes may scrub each other sufficiently, thereby increasing the potential of the charge imparted to the toner. The present invention determines the distance between the adjacent developing brushes, the distance between the brush and the image developing surface on the photosensitive member, the distance between the brush and the brush shaping plate and the distance between the brush and the magnetic field adjusting plate in order to provide the optimum conditions for accomplishing the above described ends.

The above andother objects features and advantages of the present invention will become more apparent from the following description of illustrative embodiments thereof taken in conjunction with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING:

FIG. 1 is a schematic sectional view of one embodiment of the present invention;

FIG. 2 is a view similarto FIG. 1 on enlarged scale;

FIG. 3 is a schematic sectional view of another embodiment of the present invention; and

FIG. 4 is a fragmentary view thereof on enlarged scale.

DESCRIPTION OF THE PREFERRED EMBODIMENTS:

Referring to FIGS. 1 and 2, within a developer chamber l are disposed a pair of rotary magnetic rollers 2, 3 in parallel with each other. As best shown in FIG. 1, N- and S-poles are alternately arranged around the circumferential surface of each of the rotary magnetic rollers 2 and 3. The rollers 2 and 3 are rotated in the opposite directions with respect to each other and toward the portion A of a photosensitive member where a latent image is developed. In the instant embodiment,

both of the rollers 2 and 3 have the same radii and rotate at the same speed in such a manner that opposite polarity poles oppose with each other. However, as long as the opposite polarity poles of the magnetic rollers 2 and 3 are opposed during the rotation of the rollers 2 and 3, any diameter and the speed of rotation may be suitably selected. In a magnetic brush developing device, magnetic carriers 4 are attracted by the magnetic rollers 2 and 3, thereby forming magnetic brushes on each of the rollers. The toner 5 is attracted to the surface of the magnetic carriers 4 so that by friction between the carriers 4 and the toner 5, a charge is imparted to the toner 5 so as to develop an electrostatic image formed upon the surface of the photosensitive member.

The novel feature which characterizes the present invention is that a hard brush layer B and a soft brush layer C .are formed on each of the magnetic rollers 2 and 3. The hard brush layer B is adapted to rub the developing surface without deteriorating the once developed image and the soft brush layer C above the hard brush layer B develops the image. This soft brush layer C serves to develop a very sharp and high quality im- Referring to FIG. 2, the present invention will be described in more detail hereinafter. The magnetic carriers which are stored in the developer chamber 1 and to which are attracted the toner 5 are attracted toward the magnetic roller 2 and 3 thereby forming the magnetic brushes D upon the surfaces of the rollers 2 and 3. The thus formed magnetic brushes D are hard brushes as a whole having various lengths and are not suited for use in direct developing because the hard brushes tend to brush off the toner image developed upon the developing surface. Therefore, it is necessary that the free ends of the hard brushes be spaced apart from the developing surface so as not to contact therewith, thereby deteriorating the image. For this purpose, the present invention provides developing brush shaping plates 6 and 7 for the magnetic rollers 2 and 3 respectively. The shaping plates 6 and 7 are disposed behind the toner supply section E adjacent the developing portion A. The free ends of the .plates 6 and 7 are spaced apart from the centers of the magnetic rollers 2 and 3 by a distance slightly shorter than the distance a between the centers of the magnetic rollers 2 and 3 and the developing surface, so that the lengths of the brushes are uniformly determined. Thus, a hard brush B having a uniform length or height is formed around the magnetic roller by the shaping plate 6 or 7 and a part of the hard brush B rises therefrom uniformly due to the magnetic strength of the magnetic roller, the centrifigual force, the attraction between the opposite polarity poles of the magnetic rollers and so on, in the path from the shaping plate to the developing surface. Furthermore, as shown in FIGS. 3 and 4, magnetic field adjusting plates 8 and 9 made of a magnetic material, are disthe soft brushes C may be uniformly formed over a wide portion of the hard brushes B between the adjacent opposite poles N and S. The thus formed soft brushes C lightly rub the developing surface thereby developing a high tone image having no developing mark. After the development by the soft brushes C, the toner will not remain upon the magnetic rollers even though the hard brushes exist and will not reach the developing surface because the distancev 0/2, c where is the distance between the centers of the magnetic rollers 2 and 3, is longer than the distance 12 between the center of the magnetic roller and the leading edge of the shaping plate. The distance c/2 is shorter than the distance a so that the magnetic brushes which have accomplished the development and consequently a less concentration of the toner thereupon contact with the mating brushes, and the opposite polarity poles of the magnetic rollers are opposed in closely spaced apart relation with each other. Therefore, the portion which have been constituting the hard brushes are raised and more intimate contact between the magnetic brushes of the magnetic rollers is'caused so that the toner or developing agent may be more uniformly distributed. Thus, one cycle of the magnetic roller operation from the formation of the magnetic brushes, the development of the image to the reformation of the magnetic brushes is accomplished. This will be described in more detail hereinafter. The magnetic rollers 2 and 3 are rotated in the opposite directions so that the developing surface is applied with the developing agent or toner by the magnetic brushes from the both directions. In other words, the image upon the developing surface is developed in both of the forward and reverse directions so that the directivity or orientation in development may be advantageously eliminated. The image is developed in its final stage in the reverse direction. That is, the direction of rotation of the magnetic brushes is opposite to that of the sensitized member so that adhesion of the magnetic substances to the sensitized member can be reduced to the minimum. As to the dispersion of the developing agent or toner which presents one of the serious problems in the conventional device, both the shaping plates and the magnetic field adjusting plates of the present invention serve as partition or shielding plates so that the dispersion of the developing agent or toner may be effectively prevented, thereby reducing the contamination of the copying machine. Next the relative positions of the components of the developing device in accordance with the present invention will be described in more detail hereinafter for the better understanding of the present invention. After extension studies, the inventor found out that the distance b between the leading edge of the shaping plate and thev center of the magnetic roller is preferably shorter by 0 to 2mm than the distance a between the center of the magnetic brush and the image developing surface. It was also found that a better image is obtained when the distance c is selected so as to be substantially equal to the distance 2a and 2b. Furthermore, the shaping plates 6 and 7 should be spaced apart from the image developing portion angularly by about forwardly thereof so that the soft brushes may be advantageously raised by the centrifugal forces at the N- and S-poles of the magnetic rollers. When the shaping plate is positioned so as to form an angle of a (less than 90) relative to the peripheral surface of the magnetic brush as shown in FIG. 2, the force acting upon the shaping plate from the magnetic brush may be advantageously reduced. When the shaping plate is positioned at an angle [3 (more than 90) so as to push the magnetic brush, the excess brushes are pushed by the leading edge of the shaping plate when the hard brush passes the shaping plate so that the raising of the soft brushes is much facilitated. When the magnetic field adjusting plates 8 and 9 are spaced apart from the shaping plates 6 and 7 by about 1 to 2 mm, there is an effect of uniformly, strongly and continuously raising the soft brushes without affecting adversely the hard brushes so that the latter will not contact with the developing surface. The distance d between the magnetic field adjusting plate and the center of the magnetic roller is gradually increased along the direction of rotation of the magnetic roller so that the raised soft brushes may be always outwardly extended and will not be forced backwardly, thereby laying the soft brushes flat again.

The advantages of the present invention may be summarized as follows:

1. Hard and soft brush layers are formed upon the magnetic roller so that the soft brush layer may be made in close contact with the developing surface of the photosensitive member whereby a high tone image having no developing mark may be obtained.

2. The hard brush layer does not contact with the developing surface so that the developed image will not be brushed off or deteriorated.

3. A plurality of magnetic rollers are used in such a manner that the poles of one magnetic roller may be normally opposed to the poles having the opposite polarity of another magnetic roller so that the hard and soft brushes are attracted with each other in the nip of the adjacent magnetic rollers and well agitated, whereby the developing agent or toner may be uniformly distributed and charged.

What is claimed is:

1. An electrophotographic developing device for forming a toner image on a photosensitive member comprising a developer chamber for storing electrophotographic developer including magnetic carrier and toner, at least one rotary magnetic roller positioned in said developer chamber, said magnetic roller having a plurality of N- and S-poles alternately arranged in the circumferential direction of said roller, magnetic brush shaping plate means disposed adjacent to the surface of the magnetic brush formed of said developer on said magnetic roller for shaping a hard magnetic brush layer to a predetermined thickness which will not contact with an image developing surface of a sensitized member, and magnetic field adjusting plate means made of a magnetic material for uniformly, strongly and continuously raising soft brushes upon said hard brush layer, and wherein the leading edge of said magnetic field ad- 5 justing plate means is spaced apart from the center of said magnetic roller by a distance longer than that between the center of said magnetic roller and the leading edge of said magnetic brush shaping plate means and said magnetic field adjusting plate means is diverged radially outwardly from said leading edge of said magnetic field adjusting plate means in the direction of rotation of said magnetic roller.

2. An electrophotographic developing device as defined in claim 1 wherein said soft brush is formed under the combined force of the magnetic field and centrifugal force of said magnetic roller and the attraction between the opposite poles.

3. An electrophotographic developing device as defined in claim 1 which comprises at least one pair of multipolar rotary magneticrollers each having a plurality of N- and S-poles alternately arranged in the circumferential direction of said roller, one of said at least one pair of magnetic rollers which develops an image faster than the other being rotated in the direction same as that of the sensitized member while the other magnetic roller being rotated in the opposite direction, and during rotation of said at least one pair of magnetic rollers, the poles having one polarity of one of said at least one pair of magnetic rollers being opposed to the poles having the other polarity of the other magnetic roller.

4. An electrophotographic developing device according to claim 1 which comprises two rotary magnetic rollers associated with said developer chamber, said magnetic rollers each having a plurality of N- and S- poles alternately arranged in the circumferential direction of said rollers, a said magnetic brush shaping plate means for shaping a hard brush formed of said developer on each of said magnetic rollers to a thickness which will not contact with an image developing surface of a photosensitive member, and a said magnetic field adjusting plate means associated with each of said magnetic rolls for forming a soft brush upon said hard brush layer on each of said magnetic rollers, half the distance between the centers of said magnetic rollers being shorter than the distance between each of said centers of said rotary rollers and said developing surface of said sensitized member, whereby said magnetic brush is scrubbed.

3,882,821 Dated May 13, 1975 Patent No.

lnventofls) HAJIMF: KATAYAMA and TORU TAKAHASHI It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

On the Title Page, insert Foreign Application Priority Data Japanese Application 17909/1969 March 8 1969 Japanese Application 72221/1969 September ll,l969- Column 4 line 9 "c where" should read --where c-;

Column 4 line 51 "extension" should read -extensive--= Signed and 8818 this sixteenth W of September 1975 [SEAL] Arrest:

RUTH C. MASON A nesting Officer C. MARSHALL DANN Commissioner of Parents and Trademarks 

1. An electrophotographic developing device for forming a toner image on a photosensitive member comprising a developer chamber for storing electrophotographic developer including magnetic carrier and toner, at least one rotary magnetic roller positioned in said developer chamber, said magnetic roller having a plurality of N- and S-poles alternately arranged in the circumferential direction of said roller, magnetic brush shaping plate means disposed adjacent to the surface of the magnetic brush formed of said developer on said magnetic roller for shaping a hard magnetic brush layer to a predetermined thickness which will not contact with an image developing surface of a sensitized member, and magnetic field adjusting plate means made of a magnetic material for uniformly, strongly and continuously raising soft brushes upon said hard brush layer, and wherein the leading edge of said magnetic field adjusting plate means is spaced apart from the center of said magnetic roller by a distance longer than that between the center of said magnetic roller and the leading edge of said magnetic brush shaping plate means and said magnetic field adjusting plate means is diverged radially outwardly from said leading edge of said magnetic field adjusting plate means in the direction of rotation of said magnetic roller.
 2. An electrophotographic developing device as defined in claim 1 wherein said soft brush is formed under the combined force of the magnetic field and centrifugal force of said magnetic roller and the attraction between the opposite poles.
 3. An electrophotographic developing device as defined in claim 1 which comprises at least one pair of multipolar rotary magnetic rollers each having a plurality of N- and S-poles alternately arranged in the circumferential direction of said roller, one of said at least one pair of magnetic rollers which develops an image faster than the other being rotated in the direction same as that of the sensitized member while the other magnetic roller being rotated in the opposite direction, and during rotation of said at least one pair of magnetic rollers, the poles having one polarity of one of said at least one pair of magnetic rollers being opposed to the poles having the other polarity of the other magnetic roller.
 4. An electrophotographic developing device according to claim 1 which comprises two rotary magnetic rollers associated with said developer chamber, said magnetic rollers each having a plurality of N- and S- poles alternately arranged in the circumferential direction of said rollers, a said magnetic brush shaping plate means for shaping a hard brush formed of said developer on each of said magnetic rollers to a thickness which will not contact with an image developing surface of a photosensitive member, and a said magnetic field adjusting plate means associated with each of said magnetic rolls for forming a soft brush upon said hard brush layer on each of said magnetic rollers, half the distance between the centers of said magnetic rollers being shorter than the distance between each of said centers of said rotary rollers and said developing surface of said sensitized member, whereby said magnetic brush is scrubbed. 